A microfluidic, or lab-on-a-chip (LOC), device is a planar device, one surface of which contains one or more of the following microfluidic features: intersecting channels, reservoirs, valves, detectors, flow switches, etc., which are fabricated using semiconductor microfabrication technology. The device surface is typically bonded to another planar surface so that the channels are enclosed except at sample and buffer input and output points. Microfluidic devices are designed for complex laboratory functions such as DNA sequencing, analytical separation and analytical measurements. The first of such devices disclosed in the patent literature were made of silicon, as described by Pace, U.S. Pat. No. 4,908,112.
Microfluidic devices are considered the enabling technology for low cost, high versatility operations, many of which find great utility in biotech and pharmaceutical industries. Applications of planar microfabricated devices primarily include using electroosmotic, electrokinetic, and/or pressure-driven motions of liquids and particles for fluid transport. The proceedings of the Micro Total Analysis Systems-2000 Symposium (A. Van Den Berg and W. Olthuis, ed., Kluwer Academic Publishers, Dordrecht (2000)) highlight the recent rapid progress in the field of microfluidics.
A common means of injecting samples into the enclosed fluid channels for analytical operations such as capillary electrophoresis (CE) is the use of intersecting channels to connect the sample reservoirs to the main fluid separation channels. The intersecting channels can be in the form of a ‘T’, as first disclosed in U.S. Pat. No. 4,908,112, or in the form of a cross, as shown in FIG. 1. Referring to FIG. 1, a sample to be injected from the sample reservoir 1 to the fluidic channel by an electrokinetically driven operation requires a voltage Vs to be applied to the sample reservoir or well. Another voltage or electrical ground Vsw is applied to the sample waste well 2, typically situated beyond the junction point of the sample injection channel and the main fluidic channel. A stream of the sample is electrokinetically transported from the sample reservoir toward the waste reservoir, intersecting the main fluidic channel connecting buffer reservoir 3 and buffer waste well 4 en route. An injection plug of sample into the main fluidic channel is formed when the voltage difference Vs-Vsw is reduced or eliminated, thus stopping the stream, and another voltage, Vb, is applied to the buffer reservoir 3 and, a voltage Vbw to the buffer waste well 4. In this mode of sample injection, a sample reservoir, a buffer reservoir and at least one waste well are typically provided. Even when only several nanoliters of sample is desired for the separation experiment, a much larger quantity of sample is typically placed in the sample reservoir to establish the flow toward the main microfluidic channel, which may be the CE separation channel.
If automatic sample filling of the device is desired, as in the case of 96-channel CE devices for high-throughput applications, a coupler such as that described in E. Meng et al., Proceedings for Micro-TAS 2000, ibid. Pp. 41-44 can be used to couple the sample from an external vessel into the sample reservoir on the device via a capillary. Once the sample is deposited into the sample reservoir, the same injection procedure as described above may be carried out.
In liquid phase applications, especially in capillary electrophoresis, the channel widths used by those skilled in the art are generally uniform in width, with the most common width being about 100 μm or smaller.
It is believed that LOC may be used to perform a variety of operations that are currently performed by other laboratory methods. Unfortunately, only few people are currently skilled in the art of making and using LOC devices. Many of the most attractive customers for LOC technology are scientists who are experts in their specific fields of science and are well-versed in performing experiments using traditional lab techniques, but who are not yet familiar with LOC. Accordingly, such scientists may need substantial guidance in converting their traditional lab techniques to LOC technology. For someone skilled in LOC technology, designing an LOC device is relatively straightforward, once certain parameters of the laboratory technique to be replicated are known. Thus, typically, an LOC technologist discusses with the laboratory scientist the parameters of the operation to be replicated via LOC, and then designs the LOC device. This approach, while effective in producing a functionally suitable device, suffers from the delay and expense inherent in arranging meetings among the parties involved. Furthermore, the cost of prototyping an LOC device with conventional microfabrication technology involving cleanroom techniques or laser cutting is expensive.
As can be appreciated from the above, there is a need for a more facile means by which the laboratory scientist can quickly identify a configuration for a microfluidic device which will perform functions that he can identify, but for which he has no design expertise, and then rapidly obtain the designed device.